Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Short-Period Variable Be Stars Discovered or Confirmed through Self-Correlation Analysis of Hipparcos Epoch Photometry
We have surveyed 277 bright Be stars for short-period (0.2-2 day)photometric variability using self-correlation analysis of Hipparcosepoch photometry. This extends the work of Percy et al.; the methods areas described there. We report the discovery, timescale, and amplitude ofshort-period variability in: HD 7636 (V764 Cas), HD 11606 (V777 Cas), HD13661 (V549 Per), HD 34921, HD 36408, HD 40978, HD 58343 (FW CMa), HD63460 (o Pup), HD 88195 (17 Sex), HD 89353 (AG Ant, HR 4049), HD 129954(CO Cir), HD 158220 (V862 Ara), HD 173219 (V947 Sct), and HD 187567(V1339 Aql). We report the confirmation of short-period variabilityusing an independent form of analysis in HD 52918 (19 Mon), HD 105382(V863 Cen), HD 137387 (κ-1 Aps), HD 157832 (V750 Ara), and HD163868 (V3984 Sgr). These include a β Cephei star (19 Mon), aVega-type star (17 Sex), and a post-asymptotic giant branch B star (HR4049). We find that short-period variability is more prevalent inearly-B stars than in late-B stars. We have found no β Cephei typevariables in our sample of Be stars, other than 19 Mon, which isapparently not a Be star.
| Strongly absorbed quiescent X-ray emission from the X-ray transient XTE J0421+56 (CI Cam) observed with XMM-Newton
We have observed the X-ray transient XTE J0421+56 in quiescence withXMM-Newton. The observed spectrum is highly unusual being dominated byan emission feature at ~ 6.5 keV. The spectrum can be fit using apartially covered power-law and Gaussian line model, in which theemission is almost completely covered (covering fraction of 0.98-0.06+0.02) by neutral material and is stronglyabsorbed with an \nh of ( 5 -2+3) x1023 atom cm-2. This absorption is local and notinterstellar. The Gaussian has a centroid energy of 6.4 +/- 0.1 keV, awidth sigma <0.28 keV and an equivalent width of 940+650-460 eV. It can be interpreted as fluorescentemission line from iron. Using this model and assuming XTE J0421+56 isat a distance of 5 kpc, its 0.5-10 keV luminosity is 3.5 x1033 erg s-1. The Optical Monitor onboardXMM-Newton indicates a V magnitude of 11.86 +/- 0.03. The spectra ofX-ray transients in quiescence are normally modeled using advectiondominated accretion flows, power-laws, or by the thermal emission from aneutron star surface. The strongly locally absorbed X-ray emission fromXTE J0421+56 is therefore highly unusual and could result from thecompact object being embedded within a dense circumstellar wind emittedfrom the supergiant B[e] companion star. The uncovered and unabsorbedcomponent observed below 5 keV could be due either to X-ray emissionfrom the supergiant B[e] star itself, or to the scattering ofhigh-energy X-ray photons in a wind or ionized corona, such as observedin some low-mass X-ray binary systems.
| Polarimetric Studies of Stars with an Infrared Emission Excess
The results of polarimetric and IR (IRAS) observations of 24 B-A-F starsare given. Intrinsic polarization of the light from 11 of the 24 starsis observed. The degree of polarization for the other 13 stars is withinthe measurement errors. Two-color diagrams are also constructed. From acomparison of the degree of polarization with the color index on thetwo-color diagrams it is seen that 8 of these 13 stars probably are ofthe Vega type, while 5 are stars with gasdust shells and/ordiskshells. It is shown that 6 of the aforementioned 11 starswith intrinsic polarization evidently are stars with gasdustshells and/or diskshells, while 5 of them (also including No. 24)are of the Vega type. It is also shown that the IR emission from 10 ofthe stars corresponds to a power-law distribution F . This fact may beexplained both by freefree transitions of electrons and bythermal emission from dust grains in circumstellar gasdust shells(disks).
| Uber die Eruptivendatenbank und einer zukunftige Datenbank aller BAV Beobachtungen.
Not Available
| GasDust Shells around Some Early-Type Stars with an IR Excess (of Emission)
The results of an investigation of IR (IRAS) observations of 58OBAF stars of different luminosity classes, whichare mainly members of various associations, are presented. The colorindices of these stars are determined and two-color diagrams areconstructed. The emission excesses at 12 and 25 mm (E 12 and E 25) arealso compared with the absorption A1640 of UV radiation. It is concludedthat 24 stars (of the 58 investigated) are disk systems of the Vegatype, to which Vega = N 53 also belongs. Eight known stars of the Vegatype are also given in the figures for comparison. The remaining 34stars may have gasdust shells and/or shelldisks. The IRemission excesses of the 34 investigated stars and 11 comparison stars(eight of them are Be-Ae stars) are evidently due both to thermalemission from grains and to the emission from freefreetransitions of electrons in the gasdust shells of these stars.
| A Search for High-Velocity Be Stars
We present an analysis of the kinematics of Be stars based uponHipparcos proper motions and published radial velocities. We findapproximately 23 of the 344 stars in our sample have peculiar spacemotions greater than 40 km s-1 and up to 102 kms-1. We argue that these high-velocity stars are the resultof either a supernova that disrupted a binary or ejection by closeencounters of binaries in young clusters. Be stars spun up by binarymass transfer will appear as high-velocity objects if there wassignificant mass loss during the supernova explosion of the initiallymore massive star, but the generally moderate peculiar velocities of BeX-ray binaries indicate that the progenitors lose most of their massprior to the supernova (in accordance with model predictions). Binaryformation models for Be stars predict that most systems bypass thesupernova stage (and do not receive runaway velocities) to createultimately Be+white dwarf binaries. The fraction of Be stars spun up bybinary mass transfer remains unknown, since the post-mass transfercompanions are difficult to detect.
| The Hard X-Ray Luminosity of OB Star Populations: Implications for The Contribution of Star Formation to the Cosmic X-Ray Background
We present an empirical analysis of the integrated X-ray luminosityarising from populations of OB stars. In particular, we utilize resultsfrom the All-Sky Monitor on RXTE, along with archival data from previousmissions, to assess the mean integrated output of X-rays in the 2-10 keVband from accreting early-type binaries within 3 kpc of the Sun. Using arecent OB star census of the solar neighborhood, we then calculate thespecific X-ray luminosity per O star from accretion-powered systems. Wealso assess the contribution to the total X-ray luminosity of an OBpopulation from associated T Tauri stars, stellar winds, and supernovae.We repeat this exercise for the major Local Group galaxies, concludingthat the total X-ray luminosity per O star spans a broad range from 2 to20×1034 ergs s-1. Contrary to previousresults, we do not find a consistent trend with metallicity; in fact,the specific luminosities for M31 and the SMC are equal, despite havingmetallicities that differ by an order of magnitude. In light of theseresults, we assess the fraction of the observed 2-10 keV emission fromstarburst galaxies that arises directly from their OB star populations,concluding that, while binaries can explain most of the hard X-rayemission in many local starbursts, a significant additional component orcomponents must be present in some systems. A discussion of the natureof this additional emission, along with its implications for thecontribution of starbursts to the cosmic X-ray background, concludes ourreport.
| Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars
We present the results of statistical analyses of a sample of 627 Bestars. The parameters of intrinsic polarization (p*),projected rotational velocity (v sin i), and near IR excesses have beeninvestigated. The values of p* have been estimated for a muchlarger and more representative sample of Be stars (~490 objects) thanpreviously. We have confirmed that most Be stars of early spectral typehave statistically larger values of polarization and IR excesses incomparison with the late spectral type stars. It is found that thedistributions of p* diverge considerably for the differentspectral subgroups. In contrast to late spectral types (B5-B9.5), thedistribution of p* for B0-B2 stars does not peak at the valuep*=0%. Statistically significant differences in the meanprojected rotational velocities (/line{vsin i}) are found for differentspectral subgroups of Be stars in the sense that late spectral typestars (V luminosity class) generally rotate faster than early types, inagreement with previously published results. This behaviour is, however,not obvious for the III-IV luminosity class stars. Nevertheless, thecalculated values of the ratio vt/vc of the truerotational velocity, vt, to the critical velocity forbreak-up, vc, is larger for late spectral type stars of allluminosity classes. Thus, late spectral type stars appear to rotatecloser to their break-up rotational velocity. The distribution of nearIR excesses for early spectral subgroups is bi-modal, the position ofthe second peak displaying a maximum value E(V-L)~ 1 . m 3for O-B1.5 stars, decreasing to E(V-L)~0. m8 for intermediatespectral types (B3-B5). It is shown that bi-modality disappears for latespectral types (B6-B9.5). No correlations were found betweenp* and near IR excesses and between E(V-L) and vsin i for thedifferent subgroups of Be stars. In contrast to near IR excesses, arelation between p* and far IR excesses at 12 mu m is clearlyseen. A clear relation between p* and vsin i (as well asbetween p* and /line{vsin i}/vc) is found by thefact that plots of these parameters are bounded by a ``triangular"distribution of p*: vsin i, with a decrease of p*towards very small and very large vsin i (and /line{vsini}/vc) values. The latter behaviour can be understood in thecontext of a larger oblateness of circumstellar disks for the stars witha rapid rotation. From the analysis of correlations between differentobservational parameters we conclude that circumstellar envelopes forthe majority of Be stars are optically thin disks with the range of thehalf-opening angle of 10degr
| On the origin of the difference between the runaway velocities of the OB-supergiant X-ray binaries and the Be/X-ray binaries
The recent finding by Chevalier & Ilovaisky (1998) from Hipparcosobservations that OB-supergiant X-ray binaries have relatively largerunaway velocities (mean peculiar tangential velocity avvt = 42 +/- 14\kms), whereas Be/X-ray binaries have low runaway velocities (avvt = 15+/- 6 \kms), provides confirmation of the current models for theformation of these two types of systems. These predict a difference inrunaway velocity of this order of magnitude. This difference basicallyresults from the variation of the fractional helium core mass as afunction of stellar mass, in combination with the conservation oforbital angular momentum during the mass transfer phase that precededthe formation of the compact object in the system. This combinationresults into: (i) Systematically narrower pre-supernova orbits in theOB-supergiant systems than in the Be-systems, and (ii) A largerfractional amount of mass ejected in the supernovae in high-mass systemsrelative to systems of lower mass. Regardless of possible kickvelocities imparted to neutron stars at birth, this combination leads toa considerable difference in average runaway velocity between these twogroups. If one includes the possibility for non-conservative masstransfer the predicted difference between the runaway velocity of thetwo groups becomes even more pronounced. The observed low runawayvelocities of the Be/X-ray binaries confirm that in most cases not morethan 1 to 2 \msun\ was ejected in the supernovae that produced theirneutron stars. This, in combinatioThe values given here are not identical (though similar) to those listedin Chevalier & Ilovaisky (1998). The corrections we applied areoutlined below.
| Spectral variability of the massive X-ray binary LSI +65(deg) 010
We present optical spectroscopic observations of the massive X-raybinary LSI +65(deg) 010, the optical counterpart to the X-ray transient2S0114+65. Our data show a dramatic variability in 1992 and only a mildvariability during 1993-1995. An increase by a factor more than three inthe equivalent width of the Hα emission line within four days ispresent in Nov. 1992. It is interesting to notice that changes havetaken place only in the blue side on Nov. 4, 1992, when compared tosimilar spectrum taken one day before. We associate this phenomenon withthe existence of an HII region around the neutron star. A double-peakprofile is seen in the spectrum of Sept. 1994. If this double-peakprofile is real, we suggest that such a profile may be explained by theemission line from an HII region around the neutron star, superposed onthat from the stellar wind of the supergiant.
| Near IR spectroscopy of candidate B[e]/X-ray binaries
We present near IR spectra (0.8-2.5 mu m) of the two candidateB[e]/X-ray binary systems CI Cam/XTE J0421+560 and HD34921/1H 0521+37.The spectra of both systems show evidence for a more complexcircumstellar environment than those seen in classical Be/X-raybinaries. Strong H i and He i emission is seen, confirming the presenceof a dense circumstellar wind; O i, Fe ii and [Fe ii] emission in CI Campoints to recombination of this wind. He ii emission, presumably due toexcitation by the compact companion is observed in CI Cam. Finally,emission is seen from Na i and CO, which implies regions of thecircumstellar environment with much lower excitation temperatures andhigher densities, shielded from direct stellar radiation. Both systemsshow evidence for continuum emission from circumstellar dust. Neither ofthese two features has previously been observed in any other classicalBe/X-ray binary system. Adopting the classification criteria of Lamerset al. (1998) we suggest identifications of unclB[e] and sgB[e] forHD34921 and CI Cam respectively, making them the first High Mass X-rayBinaries with primaries showing the B[e] phenomenon known.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Catalogue of H-alpha emission stars in the Northern Milky Way
The ``Catalogue of Stars in the Northern Milky Way Having H-alpha inEmission" appears in Abhandlungen aus der Hamburger Sternwarte, Band XIin the year 1997. It contains 4174 stars, range {32degr <= l() II< 214degr , -10degr < b() II < +10degr } having the Hαline in emission. HBH stars and stars of further 99 lists taken from theliterature till the end of 1994 were included in the catalogue. We givethe cross-identification of stars from all lists used. The catalogue isalso available in the Centre de Données, Strasbourg ftp130.79.128.5 or http://cdsweb.u-strasbg.fr and at the HamburgObservatory via internet.
| On the nature of Be/X-ray binaries
It has been suggested that most Be/X-ray binaries are low X-rayluminosity nearby objects, containing white dwarfs (Chevalier &Ilovaisky 1998). We show that existing evidence indicates that all knownBe/X-ray binaries are relatively bright X-ray sources containing neutronstars and that the spectral distribution of this group differsconsiderably from that of isolated Be stars. We suggest that thedifferent X-ray properties of the systems can be explained by the sizesof the orbits of the neutron stars. Systems with close orbits are brighttransients which show no quiescent emission as a consequence ofcentrifugal inhibition of accretion. Systems with wide orbits arepersistent sources and display no large outbursts. Systems withintermediate orbits present a mixture of both behaviours.
| Dust shells around certain early-type stars with emission lines.
Not Available
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| HIPPARCOS results on massive X-ray binaries
We present results on parallaxes, magnitudes and proper motions for 17optically identified massive X-ray binaries (MXRB) which were observedduring the Hipparcos astrometry mission. This sample includes thesources detected in the medium-energy range (2-10 keV) having opticalcounterparts brighter than V=12. We compare the Hipparcos results withground-based optical data and derive probable values for absolutemagnitudes and peculiar tangential velocities (vt). The 4 OBsupergiant systems in our sample are high-velocity objects (the averagevalue of vt is greater than 60 km/s), while the 13 Be systemshave low velocities ( = 11.3 +/- 6.7 km/s),suggesting a different formation mechanism for the two subgroups. Theunusual X-ray/radio source LSI+61(deg) 303 lies much closer thanpreviously believed and its low optical luminosity (MV =+2.2) and blue intrinsic colors now suggest it may be a peculiar type oflow-mass X-ray binary.
| Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
| A Spectral Atlas of Hot, Luminous Stars at 2 Microns
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..107..281H&db_key=AST
| Rotational Velocity Determinations for 164 Be and B Stars
Rotational velocities, v sin i, have been obtained for 96 Be and 68normal B stars by measurements of the FWHM of the He I lambda-4471 line(for spectral types B0-B4.5) and Mg II lambda-4481 (for types B5-B9.5).The consistency of various published sources is examined. (SECTION:Stars)
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Optical emission line profiles from BeXRBs.
Not Available
| X-Ray Emission from Be Star/X-Ray Binaries
Not Available
| The distribution of OB stars in the directions of the stellar associations AUR OB 1 and 2
Forty two OB stars have been observed with the space telescope Glazar at1640 A in an area of about 17 sq deg in the direction of the stellarassociations Aur OB 1 and 2. Twenty five of the observed stars of knownspectral type and with colorimetric data are assigned to four stargroups: a B association at a distance of 600 pc and three O associationsat distances of 1100, 2000 and 3000 pc respectively, designated Aur B0.6, Aur OB 1.1, Aur OB 2.0, and Aur OB 3.0. Fourteen stars of unknownspectral type should be OB or at least early-A-type stars, since theirimages were obtained on photographs taken with Glazar. The latestpossible spectral types of these stars and also of stars for which thespectral types are known only roughly are determined. There is a more orless uniform dust cloud in front of the dense parts of the three distantassociations, which introduces an extinction of about 3.5 mag at 1640 A.
| IRAS sources beyond the solar circle. III - Observations of H2O, OH, CH3OH and CO
We have used the 100-m Effelsberg and 32-m Medicina radiotelescopes tosearch for H2O maser emission (22.235 GHz) towards 1143 IRAS sources,for OH (1665/67 MHz) towards 303 IRAS sources, and for CH3OH (12.179GHz) towards 19 IRAS sources. The IRAS sources have been selected tohave colors of premain sequence objects. To obtain an estimate of thekinematic distance, we observed (C-12)O (J = 2 to 1) and (C-12)O (J = 3to 2) with the KOSMA 3-m telescope towards 25 sources showing H2Oemission and not yet observed in CO. This paper presents theobservational results in form of tables with line parameters or upperlimits and spectra of detected sources.
| Rapid line variability of BD + 37 deg 1160, a possible optical counterpart of the X-ray source 1H 0521 + 373
Spectroscopic observations of the peculiar Be star BD + 37 deg 1160, thepossible optical counterpart of the hard X-ray source 1H 0521 + 373 arereported. The present data show rapidly variable Fe II and Balmer lineemission. The presence of short time line variability (time scale notgreater than 300 s) suggests that the origin of the phenomenon can bedue to the presence of a compact companion.
| BD + 37 deg 1160 - A probable optical counterpart of the X-ray source 1H 0521 + 373
Results are reported on detailed X-ray, UV, optical, and IR observationsof two stars: BD + 37 deg 1146 and BD + 37 deg 1160. These data suggestthat the star BD 37 deg 1160 is the optical counterpart of the X-raysource 1H 0516 + 373. It is shown that the optical spectrum of this stardisplays rapidly variable emision features, an IR excess emission, and astrong similarity to X Per, which also has a similar hard X-rayspectrum.
| A survey of Be stars in the 7500-8800 A region
This survey covers the spectra of over 97 Be stars observed at 50 and230 A/mm plate factors with a Reticon in the 7500-8800 A region.Equivalent widths were measured for the strongest lines present in thisregion. Although the Be stars have been well studied in the classic3800-4800 A region, there exist fewer studies of the 7500-8800 A region,which shall be referred to as the 'near-infrared'. The interest of thenear infrared region lies in the fact that several strong features arepresent, namely the higher lines of the Paschen series of H I, two O Ifeatures, and the Ca II triplet. The behavior of these features is oftendifferent from that observed in normal stars, for instance the Ca II. Itis the purpose of the present paper to provide a systematic survey. Toachieve this, a sample of 100 Be and B-type shell stars selected fromJaschek et al. (1980) have been observed.
| The interstellar 217 NM band - A third catalogue of equivalent widths
A catalog of equivalent widths of the 217 nm interstellar absorptionband as well as other parameters characterizing the extinction curve inthe ultraviolet has been compiled for 790 O and B stars. A relativelytight correlation between the equivalent width of the 217 nm band andE(B-V) indicates that the absorber of this band is connected with thepopulation of larger interstellar grains responsible for the visualextinction. The parameter characterizing the amount of extinction in thefar UV is only weakly correlated with E(B-V), a result in accord withthe assumption that a second population of very small grains causes therapid increase of the far-UV extinction.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Arabaci |
| Sað Açýklýk: | 05h22m35.23s |
| Yükselim: | +37°40'33.6" |
| Görünürdeki Parlaklýk: | 7.447 |
| Uzaklýk: | 2564.103 parsek |
| özdevim Sað Açýklýk: | -0.2 |
| özdevim Yükselim: | -7 |
| B-T magnitude: | 7.61 |
| V-T magnitude: | 7.461 |
Kataloglar ve belirtme:
|
INHABITED SKY
